Abstract
The ionization potentials of the transient species CH3CH2O, CH3CHOH, and CH2CH2OH (generated by the F+ethanol reactions) are measured by photoionization mass spectrometry: I.P.(CD3CD2O)=10.29±0.08 eV (tentative), I.P.(CH3CHOH)<6.85 eV, and I.P.(CD2CH2OH) ≤8.35±0.06 eV. The latter results in a cation of uncertain structure. These reactions also generate vinyl alcohol (adiabatic I.P.=9.33±0.01 eV) and acetaldehyde. A redetermined appearance potential of CH3CHOH+ from ethanol enables one to infer the proton affinity of acetaldehyde to be ≥183.8±0.2 kcal/mol and an α (C–H) bond energy in ethanol ≳91.1 kcal/mol (0 K). The appearance potential of m/e=45 ion from bromoethanol is interpreted as formation of a C2H5O+ isomer having the oxirane structure, with ΔHf00 of ∼173.9 kcal/mol, consistent with earlier alternative measurements. A second increase in the m/e=45 ion yield curve from ethanol is interpreted as formation of this same isomer. This interpretation, and an alternative cycle, lead to a β (C–H) bond energy in ethanol of 98±2 kcal/mol. The implication of the current results to the dynamics of dissociation of ethanol cations is discussed.
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